This invention relates generally to vision systems for vehicles and, more particularly, to rearview vision systems which provide the vehicle operator with scenic information in the direction rearward of the vehicle. More particularly, the invention relates to a rearview vision system utilizing image capture devices, such as CMOS imaging arrays and the like.
A long-felt need in the art of vehicle rearview vision systems has been to eliminate exterior rearview mirrors by utilizing image capture devices, such as cameras, in combination with dashboard displays. This would be beneficial because it would reduce wind drag on the vehicle, wind noise and vehicle weight. Furthermore, rearview mirrors protrude a substantial distance from the side of the vehicle, which makes maneuvering in tight spaces more difficult. Image capture devices are capable of positioning in a greater variety of locations on the vehicle, providing more flexibility of vehicle styling. It is further expected that camera systems would greatly reduce the blind spots to the sides and rear of the vehicle common with vehicles equipped with conventional rearview mirror systems. The driver cannot perceive vehicles, objects, or other road users in such blind spots without turning his or her body, which interferes with forward-looking visual activities.
Camera-based rearview vision systems for vehicles have not obtained commercial acceptance. One difficulty with proposed systems has been that they present a large amount of visual information in a manner which is difficult to comprehend. This difficulty arises from many factors. In order to significantly reduce blind spots, multiple image capture devices are typically positioned at various locations on the vehicle. The image of an object behind the equipped vehicle is usually captured by more than one image capture device at a time and displayed in multiple images. This may confuse the driver as to whether more than one object is present. When multiple image capture devices are positioned at different longitudinal locations on the vehicle, objects behind the vehicle are at different distances from the image capture devices. This results in different image sizes for the same object. This effect is especially noticeable for laterally extending images, such as a bridge, highway crosswalk markings, the earth's horizon, and the like. Such images are at different vertical angles with respect to the image capture devices. This results in different vertical positions on the display causing the elongated image to appear disjointed.
A camera system provides a monocular view of the scene, compared to the binocular, or stereoscopic, view obtained when the scene is viewed through a rearview mirror. This makes the ability to judge distances in a camera system a problem. This effect is most noticeable at distances close to the vehicle where stereoscopic imaging is relied upon extensively by the driver in judging relative locations of objects. Therefore, known camera systems fail to provide to the driver important information where that information is most needed--at small separation distances from surrounding objects.
Another difficulty with camera systems is that, in order to provide a sufficient amount of information, the camera system typically presents the driver with a greatly increased field of view. This improves performance by further reducing blind spots at the side and rear of the vehicle. However, an increased field of view is often obtained by utilizing a wide-angle lens which introduces distortion of the scene and further impairs the ability of the driver to judge distances of objects displayed. The problem with such distortion of the scene is that the driver must concentrate more on the display and take a longer time to interpret and extract the necessary information. This further distracts the driver from the primary visual task of maintaining awareness of vehicles and other objects in the vicinity of the driven vehicle.